Thermo-mechanical behavior of epoxy shape memory polymer foams

Abstract

Shape memory polymer foams have significant potential in biomedical and aerospaceapplications, but their thermo-mechanical behavior under relevant deformation conditionsis not well understood. In this paper we examine the thermo-mechanical behavior of epoxyshape memory polymer foams with an average relative density of nearly 20%. Thesefoams are deformed under conditions of varying stress, strain, and temperature.The glass transition temperature of the foam was measured to be approximately90 °C and compression and tensile tests were performed at temperatures ranging from 25 to125 °C. Various shape recovery tests were used to measure recovery properties under differentthermo-mechanical conditions. Tensile strain to failure was measured as a function oftemperature to probe the maximum recovery limits of the foam in both temperature andstrain space. Compression tests were performed to examine compressibility of the materialas a function of temperature; these foams can be compacted as much as 80% and stillexperience full strain recovery over multiple cycles. Furthermore, both tensile strain to failuretests and cyclic compression recovery tests revealed that deforming at a temperature of80 °C maximizes macroscopic strain recovery. Deformation temperatures above or below thisoptimal value lead to lower failure strains in tension and the accumulation ofnon-recoverable strains in cyclic compression. Micro-computed tomography (micro-CT)scans of the foam at various compressed states were used to understand foam deformationmechanisms. The micro-CT studies revealed the bending, buckling, and collapse of cellswith increasing compression, consistent with results from published numerical simulations.